While there might not be one particular crystal that's The Strongest One, it might help to remember that the form of the crystal does have an impact on the way it radiates energy.

Natural crystals seem to offer the most potent, or at least most focused, energies. I've taken advantage of quartz points' ability to kind of "laser" their energy in the needed direction. Carved crystals have softer energies -- I've seen their energies described as being "softer" around the edges.

So maybe if someone finds the energies of a natural crystal to be a bit too much of a good thing at a given moment, they could try a carved or tumbled stone instead. Maybe they'll feel more comfortable with the energies of the same mineral if it's been made into a tumblestone, a sphere, or some other shape.